This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-094619 filed on Mar. 30, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to vehicle seats. More particularly, the present invention pertains to a lumbar support device in the seat back of a vehicle seat for supporting an occupant""s lumbar region.
UK Patent GB2316604 published in 1998 discloses a lumbar support device for a vehicle seat. The disclosed lumbar support device is accommodated in the seat back of the vehicle seat and includes an approximately inverse or upside down U-shaped seat back frame (a seat frame), a plane spring body disposed within the inverse U-shaped seat frame, and a plurality of wire links stretched between the seat frame and an outer peripheral frame portion of the plane spring body. The wire links suspend the plane spring body with respect to the seat frame for supporting a load from the occupant""s weight.
The lumbar support device also includes a manually operable mechanism for adjusting the tension applied to the wire links that are engaged with the seat frame at a position corresponding to an occupant""s lumbar region. Therefore, the portion of the seating surface corresponding to the occupant""s lumbar region can be adjusted rearward and forward by operation of the adjusting mechanism. When an operation force is applied to outwardly pull the wire links which suspend the plane spring body, the increase in the tension of the wire links causes the wire links to approach a parallel position with the plane spring body. However, by virtue of the construction of the support device, increasing the operation force applied to the wire links increases does not significantly increase the force component for pushing the plane spring body toward the occupant""s lumbar region. Therefore, the lumbar support device is not able to provide a good operational feeling to the occupant at its forward position. Also, due to the construction of the support device, the lumbar support device cannot exert sufficient stiffness for maintaining the seating surface at the forward position.
A need thus exists for an improved vehicle seat lumbar support device for supporting an occupant""s lumbar region.
According to one aspect of the invention, a lumbar support device for a vehicle seat includes a seat back that is adapted to support an occupant of the vehicle seat, a seat back frame provided in the seat back and including a pair of side frames and an end frame portion connected to each side frame, a plane spring body disposed within the seat back frame, a plurality of hanger springs disposed between the plane spring body and the seat back frame to suspend the plane spring body from the seat back frame, a driving device for moving a part of the plane spring body in the rearward and forward directions of the seat back, and a housing secured to at least one of the side frames. A link mechanism that is rotatably supported by a shaft fixed to the housing includes first and second arm portions extending away from the shaft. One end of the first arm portion is pivotally connected to the plane spring body and one end of the second arm portion is engaged with the driving device.
According to another aspect of the invention, a vehicle seat includes a seat cushion, a seat back having a front surface, an outer frame member positioned in the seat back, an inner frame member positioned within the outer frame member and supported on the outer frame member by a plurality of springs, a shaft mounted within the seat cushion, a torsion spring rotatably mounted for rotation relative to the shaft, the torsion spring including an arm that engages one of the side frame members, and a motor operatively connected to the torsion spring to rotate the torsion spring and the arm to cause the inner frame member to move in a direction toward the front surface of the seat back.
According to a further aspect of the invention, a lumbar support device for a vehicle seat includes a frame member positionable in a seat back of a vehicle seat, a spring body supported on the frame member and being comprised of side frame portions and at least one spring element extending between the side frame portions, and an arm rotatably positioned on a shaft that is mounted in a housing, with the arm being connected to one of the side frame portions. A driving device is operatively connected to the arm to rotate the arm and move the spring body in a forward direction to change the degree of lumbar support.